There are various pilot operated two-way valves disclosed in the prior art, some examples of which are shown in U.S. Pat. Nos. 2,969,088; 3,799,497; 4,526,340 and 4,592,533. However, prior pilot operated two-way valves known to the applicant were not capable of blocking flow in both directions when closed and allowing flow in either direction when opened. There are some bi-directional valves in which the solenoid operates directly on a spool or poppet. However, because of the limited magnetic force produced by the solenoid, such direct acting valves can only have a small poppet and are only adapted to pass relatively low flows, for example up to five or six gallons per minute.
There are hydraulic systems, for example systems including hydraulic actuators or hydraulic motors where it is desired to operate the hydraulic actuator or motor in both directions and to selectively lock the actuator or motor in a moved position. Valves which are directly actuated by a solenoid are not suitable for such applications since they do not have sufficient flow capacity to enable rapid movement of the actuator or motor in either direction. While prior art pilot operated poppet valves can be made with adequate flow capacity to enable use in such systems, a single such valve would not be effective to hydraulically lock the actuator or motor in both directions, and it was common practice to use two such valves, one in each line to the actuator or motor.